The fraction of radiation dose from neutrons received by radiation workers is increasing as a result of growth in the nuclear power industry, the development of nuclear reactor technology, and the potential use of neutrons for radiotherapy. Unfortunately, neutron dosimetry has been a difficult problem due to low neutron sensitivity and energy dependence of existing dosimetry methods. Prior art neutron dosimetry methods include thermoluminescence dosimetry (TLD), solid track detector methods using, for example, electrochemically etched CR-39 foil or NTA film, and fluid track detector methods using, for example, superheated bubble detectors (SSD).
The foregoing methods may not have the energy response and sensitivity necessary to meet the more exacting needs of neutron dosimetry. TLD suffers from high energy dependence, which may result in an error of as much as a factor of ten or more if the neutron energy spectrum is not known. NTA films have response functions that may cause even greater errors for many operational situations. Major unaddressed problems with CR-39 are the lack of sensitivity at low neutron energies, energy dependence and poor sensitivity at high energies. The more recently developed superheated drop detector has been shown to suffer from serious drawbacks including a fourfold reduction in the energy response at energies from 0.144 MeV to 5 MeV.
Other neutron dosimetry methods that have been proposed rely on electrical property changes, such as soft errors which arise in dynamic random access memories (DRAMs) through interaction with charged particles, particularly, alpha particles. For use as a neutron dosimeter, a converter is used to interact with the neutrons and generate protons or alpha particles. Accordingly, the overall performance of the neutron dosimeter is at least in part dependent on the performance of the converter which may be a foil layer applied to the DRAM. Moreover, a neutron/alpha converter has the disadvantage of increasing the dosimeter size and complicating the dose reading interpretation. In addition to the need for a converter, the material of the DRAMs is not tissue equivalent and there still remains the problem of energy dependence.
Neutron dosimetry is recognized as being a difficult problem in health physics. Recently there has been a reevaluation of the biological hazards associated with neutron exposure and, consequently, there is an urgent need for a neutron dosimetry method that provides precise neutron dose measurement over a wide range of neutron energies. More particularly, a need exists for a neutron dosimeter and dosimetry method that solves the two major unsolved problems of neutron dosimetry: (1) inability to measure the neutron energy which results in errors in estimating the dose equivalent and (2) poor sensitivity at high and low neutron energies. There is needed a neutron dosimeter that is sensitive at both high and low energies and is capable of characterizing the exposure energy spectrum, thereby to permit accurate neutron dose measurements.